US4145295A - Cellulose ester ultra-filtration membranes and their manufacture - Google Patents
Cellulose ester ultra-filtration membranes and their manufacture Download PDFInfo
- Publication number
- US4145295A US4145295A US05/824,642 US82464277A US4145295A US 4145295 A US4145295 A US 4145295A US 82464277 A US82464277 A US 82464277A US 4145295 A US4145295 A US 4145295A
- Authority
- US
- United States
- Prior art keywords
- gelation
- water
- alcohol
- ultra
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000012528 membrane Substances 0.000 title claims abstract description 96
- 238000000108 ultra-filtration Methods 0.000 title claims abstract description 28
- 238000004519 manufacturing process Methods 0.000 title abstract description 4
- 229920002678 cellulose Polymers 0.000 title 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 88
- 238000001879 gelation Methods 0.000 claims abstract description 81
- 235000019441 ethanol Nutrition 0.000 claims abstract description 60
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 49
- 230000004907 flux Effects 0.000 claims abstract description 43
- 229920000642 polymer Polymers 0.000 claims abstract description 12
- 239000010409 thin film Substances 0.000 claims abstract description 4
- 238000005266 casting Methods 0.000 claims description 31
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 30
- 239000000203 mixture Substances 0.000 claims description 24
- 239000002904 solvent Substances 0.000 claims description 23
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 20
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 18
- 239000000243 solution Substances 0.000 claims description 17
- 230000008569 process Effects 0.000 claims description 16
- 239000010408 film Substances 0.000 claims description 13
- 229910052943 magnesium sulfate Inorganic materials 0.000 claims description 10
- 238000002386 leaching Methods 0.000 claims description 9
- 229920002301 cellulose acetate Polymers 0.000 claims description 7
- 150000002148 esters Chemical class 0.000 claims description 7
- 150000001298 alcohols Chemical class 0.000 claims description 6
- MPCRDALPQLDDFX-UHFFFAOYSA-L Magnesium perchlorate Chemical compound [Mg+2].[O-]Cl(=O)(=O)=O.[O-]Cl(=O)(=O)=O MPCRDALPQLDDFX-UHFFFAOYSA-L 0.000 claims description 5
- 150000002894 organic compounds Chemical class 0.000 claims description 4
- 239000000654 additive Substances 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 3
- 235000019341 magnesium sulphate Nutrition 0.000 claims description 3
- 230000000996 additive effect Effects 0.000 claims description 2
- 230000006872 improvement Effects 0.000 claims description 2
- 150000001875 compounds Chemical class 0.000 abstract description 11
- 239000003570 air Substances 0.000 description 20
- 238000000926 separation method Methods 0.000 description 20
- 238000001223 reverse osmosis Methods 0.000 description 18
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 15
- 238000000935 solvent evaporation Methods 0.000 description 15
- 239000011148 porous material Substances 0.000 description 13
- 230000007423 decrease Effects 0.000 description 10
- 239000003921 oil Substances 0.000 description 9
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 8
- 239000000839 emulsion Substances 0.000 description 7
- ZHNUHDYFZUAESO-UHFFFAOYSA-N Formamide Chemical compound NC=O ZHNUHDYFZUAESO-UHFFFAOYSA-N 0.000 description 6
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 6
- 239000010730 cutting oil Substances 0.000 description 6
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 4
- 239000003245 coal Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000012527 feed solution Substances 0.000 description 3
- JEGUKCSWCFPDGT-UHFFFAOYSA-N h2o hydrate Chemical compound O.O JEGUKCSWCFPDGT-UHFFFAOYSA-N 0.000 description 3
- -1 nickel chloride Chemical class 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 229910021586 Nickel(II) chloride Inorganic materials 0.000 description 2
- 229920002472 Starch Polymers 0.000 description 2
- 239000012080 ambient air Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- IDGUHHHQCWSQLU-UHFFFAOYSA-N ethanol;hydrate Chemical compound O.CCO IDGUHHHQCWSQLU-UHFFFAOYSA-N 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 235000011187 glycerol Nutrition 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 235000010755 mineral Nutrition 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- QMMRZOWCJAIUJA-UHFFFAOYSA-L nickel dichloride Chemical compound Cl[Ni]Cl QMMRZOWCJAIUJA-UHFFFAOYSA-L 0.000 description 2
- 229920001592 potato starch Polymers 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 235000019698 starch Nutrition 0.000 description 2
- 239000008107 starch Substances 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 241001573946 Psara Species 0.000 description 1
- 241000212342 Sium Species 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 239000000440 bentonite Substances 0.000 description 1
- 229910000278 bentonite Inorganic materials 0.000 description 1
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 description 1
- 239000008280 blood Substances 0.000 description 1
- 210000004369 blood Anatomy 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010612 desalination reaction Methods 0.000 description 1
- 238000000502 dialysis Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000003995 emulsifying agent Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 235000001055 magnesium Nutrition 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 229940091250 magnesium supplement Drugs 0.000 description 1
- LFCFXZHKDRJMNS-UHFFFAOYSA-L magnesium;sulfate;hydrate Chemical compound O.[Mg+2].[O-]S([O-])(=O)=O LFCFXZHKDRJMNS-UHFFFAOYSA-L 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 1
- YGSFNCRAZOCNDJ-UHFFFAOYSA-N propan-2-one Chemical compound CC(C)=O.CC(C)=O YGSFNCRAZOCNDJ-UHFFFAOYSA-N 0.000 description 1
- OVARTBFNCCXQKS-UHFFFAOYSA-N propan-2-one;hydrate Chemical compound O.CC(C)=O OVARTBFNCCXQKS-UHFFFAOYSA-N 0.000 description 1
- 235000018102 proteins Nutrition 0.000 description 1
- 102000004169 proteins and genes Human genes 0.000 description 1
- 108090000623 proteins and genes Proteins 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 150000003384 small molecules Chemical class 0.000 description 1
- 239000000344 soap Substances 0.000 description 1
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 235000013343 vitamin Nutrition 0.000 description 1
- 239000011782 vitamin Substances 0.000 description 1
- 229940088594 vitamin Drugs 0.000 description 1
- 229930003231 vitamin Natural products 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/08—Polysaccharides
- B01D71/12—Cellulose derivatives
- B01D71/14—Esters of organic acids
- B01D71/16—Cellulose acetate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0011—Casting solutions therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0016—Coagulation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/14—Ultrafiltration; Microfiltration
- B01D61/145—Ultrafiltration
Definitions
- This invention relates to cellulosic-ester semi-permeable membranes, and their preparation and more particularly to semi-permeable membranes for use in ultra-filtration techniques.
- Cellulosic-ester polymer semi-permeable membranes have been developed in recent years for use in the process known as reverse osmosis for the separation of solvents and solutes as, for example, in the desalination of sea water, and in the removal of salts, such as nickel chloride, from the effluent of plating processes and the like.
- the principal aim is to achieve maximum "rejection” of solute at reasonable “flux.”
- the term "rejection” is defined as the percentage of solute removed, this being determined by the expression (1 - (C p /C b )) ⁇ 100 where C p is the concentration of the solute in the solvent after it has passed through the membrane and C b is the initial solute concentration.
- Flux is defined as the amount of solvent permeating through the membrane per unit surface area per unit time at a constant specified pressure. Flux rates of the order of 40-90 gals./sq.ft./day at 1000 psig operating pressure or 10-50 gals./ft. 2 /day at 500 psig, are considered acceptable in most reverse osmosis systems.
- reverse osmosis semi-permeable membranes are produced by casting, from a solution of a cellulosic-ester polymer in a suitable volatile solvent onto a supporting surface, generally a glass or other plate if a flat membrane is required or a tubular sheath if a tubular membrane is required, and allowing the volatile solvent to evaporate partially from the cast membrane and thereafter treating the partially dried cast membrane in a gelation bath with an aqueous solution of a polar compound, organic or inorganic, which does not react chemically with the polymer or the volatile solvent and which is miscible with the volatile solvent, so as to leach out the solvent and any additives from the cast membrane and thereby leave a porous structure in the membrane.
- a polar compound, organic or inorganic which does not react chemically with the polymer or the volatile solvent and which is miscible with the volatile solvent
- Suitable polar compounds include lower alcohols such as methanol, ethanol and propanol; dihydric compounds such as ethylene glycol, trihydric solvents such as glycerine and mixtures of any of the foregoing. It has been found that the pore size can be controlled by, among other parameters, selecting the concentration of the polar compound and hence the flux and rejection characteristics can be modified. As the concentration of the polar compound increases, the flux falls to a minimum and the rejection rate rises to a maximum, depending upon the pressure and the specific compositions involved. We have found that there comes a point, however, where a remarkable and totally unexpected reversal of the aforementioned generalization occurs and which will hereinafter be referred to as the "initial minimum".
- ultra-filtration membranes used industrially for such purposes as the treatment of oily waste waters for pollution control, blood dialysis and treatment of mineral tailings ideally require both high rejection rates (of the order of 96%) and high throughputs, i.e. flux rates of the order of 100 to 10,000 gals./ft. 2 /day at operating pressures of the order of 100 psi or lower.
- the size of the "solute” is generally far larger than that in reverse osmosis systems and such "solute” may be organic or inorganic.
- organic "solutes,” such as starch, vitamins, proteins and the like have extremely high molecular weights (in excess of 15,000) but in certain circumstances relatively low molecular weight compounds, such as oils, may be successfully treated.
- Ultra-filtration techniques can also be applied to colloidal suspensions, mixtures and emulsions which include oils, inorganic materials such as finely divided coal or mineral tailings, and the like.
- Another object of the present invention is to provide a process for producing an ultra-filtration membrane having a flux rate selected from within the approximate range 14-10,000 gals/sq. ft./day at 100 psig, at high rejection rates for selected solutes.
- a process for producing a cellulosic ester semi-permeable membrane wherein a thin film is cast from a mixture comprising cellulosic ester polymer, pore forming additive and casting solvent, a portion of the casting solvent is removed from the film and the film is immersed in a gelation bath containing a polar organic compound which is miscible with said casting solvent, the improvement, for producing an ultra-filtration membrane, comprising controlling the temperature of said gelation bath at a selected temperature in the range -20° C. to +30° C. and selecting the concentration of said polar compound in said gelation bath to be greater than that required to produce the initial minimum flux for said membrane.
- a cellulosic ester ultra-filtration membrane produced as hereinabove defined, having a flux rate in the range 14-10,000 gals./sq. ft./day at 100 psig.
- FIG. 1 is a graph illustrating flux and rejection rates (for NaCl at 1000 psig) according to the prior art
- FIG. 2(a) is a graph relating product rate (flux in gal./sq. ft./day at 100 psig) against ethyl alcohol content of the gelation bath, at various gelation bath temperatures,
- FIG. 2(b) is a similar graph showing MgSO 4 separation against ethyl alcohol content of the gelation bath at the gelation bath temperatures illustrated in FIG. 2(a);
- FIG. 3 is a graph similar to FIG. 2(a) relating product rate to ethyl alcohol content for a different membrane system.
- FIG. 1 illustrates that as the percentage of ethyl alcohol in the gelation bath increases towards about 50%, the flux in gals./sq. ft./day at 1000 psig falls to a minimum while at the same time the rejection rate rises to a maximum beyond which further gains in rejection are negligible for the type of solute under consideration. Similar curves for flux and rejection rates at 500 psig have been produced and, as expected, are generally somewhat lower in absolute terms. Even lower values would be anticipated at 100 psig, the pressure level illustrated in FIGS. 2(a) and 2(b).
- FIGS. 2(a) and 2(b) are graphs illustrative of the present invention and it will be observed that region A in both FIGS. 2(a) and 2(b) corresponds generally to the shape of the curves illustrated in FIG. 1, i.e. as ethyl alcohol concentration increases the flux falls to a minimum and the rejection rate rises to a maximum, although, at the pressure and with the specific compositions involved, the mole fraction or volume of ethyl alcohol required to achieve the respective minimum and maximum is different.
- the initial minimum hereinafter referred to as "the initial minimum"
- FIGS. 1 and 2 illustrate product flow or flux rates at pressures which differ by an order of magnitude, and at the lower pressure of FIG. 2, the whole of the curve illustrated in FIG. 1, i.e. up to about 50% ethyl alcohol in the gelation bath, has been compressed into region A, i.e. up to about 20% by volume ethyl alcohol, in FIG. 2. It is believed, therefore, that although pore size and product rate are clearly related, such relationship is not linear and not entirely predictable.
- ethyl alcohol is preferred in gelation baths according to the present invention
- polar organic compounds such as monohydric alcohols such as methanol, isopropanol, dihydric solvents such as ethylene glycol and trihydric solvents such as glycerine are also suitable. Mixtures of such polar compounds may also be used.
- composition of a cellulosic ester membrane for ultra-filtration use (solvent/polymer and non-solvent/polymer ratios of the order of 4.26 and 1.5) generally differs somewhat from that conventionally employed for reverse osmosis use (solvent/polymer and non-solvent/polymer ratios of the order of 3.01 and 0.495). It has been found that a casting solution comprising:
- magnesium perchlorate 1.3-3.3 wt.%
- magnesium perchlorate 2.3 wt.%
- the casting solution for ultra-filtration membranes and reverse osmosis is preferably cast at ambient temperature (about 18°-26° C.).
- ambient temperature about 18°-26° C.
- the ultra-filtration membrane film is immersed in a gelation bath containing an organic solvent, such as ethyl alcohol, in an amount from 25-100% by volume and preferably 55-95%.
- an organic solvent such as ethyl alcohol
- the balance of the gelation bath, if any, is conveniently water.
- the temperature of the gelation bath should be in the range -20° C. to +30° C. and no post heating is generally required.
- the membranes described therein may be made in either a batch mode or in a continuous mode in which the casting solution is continuously fed onto a casting surface and thereafter gelled and leached on a continuous basis.
- a film casting solution comprising:
- magnesium perchlorate 2.3% by wt.
- Temperature of casting solution ⁇ 22° C. (room temperature);
- Air flow rate 28 cc/sec.
- Temperature of solvent evaporation zone ⁇ 22° C. (room temperature);
- Length of solvent evaporation zone 6 to 15 inches as indicated;
- Atmosphere of above zone air, or air + acetone vapor or air + (acetone + water) vapor as indicated;
- Gelation bath flowing water, or acetone + water mixture or ethyl alcohol + water mixture, as indicated;
- Temperature of gelation bath 0° to 22° C. as indicated;
- Leaching bath water at 0° to 1° C.
- Leaching time 1 hour.
- Temperature of casting solution ⁇ 22° C. (room temperature);
- Temperature of solvent evaporation atmosphere ⁇ 22° C. (room temperature);
- Solvent evaporation atmosphere air, or air + (acetone + water) vapor, as indicated;
- Solvent evaporation time 0 to 5 seconds
- Gelation bath water or (ethyl alcohol + water) mixture as indicated;
- Temperature of gelation bath -15° to +20° C. as indicated;
- Leaching bath water at ⁇ 1° C.
- Temperature of casting solution ⁇ 22° C. (room temperature);
- Temperature of solvent evaporation atmosphere ⁇ 22° C. (room temperature);
- Solvent evaporation atmosphere ambient air, relative humidity: 85-90%;
- Solvent evaporation time 0 to 5 seconds
- Gelation bath water, or (ethyl alcohol + water) mixture or absolute ethyl alcohol as indicated;
- Temperature of gelation bath -20° C. to 30° C. as indicated;
- Leaching bath water at ⁇ 1° C.
- Leaching time 1 hour.
- Gelation bath 50% (by volume) of methanol, ethanol, isopropanol, or ethylene glycol in water-alcohol mixture;
- Table II sets forth comparable data in respect of flat membranes prepared in accordance with Example 1(b).
- FIGS. 2(a) and 2(b) set forth data in respect of flat membranes prepared in accordance with Example 1(c) and Table III sets forth data in respect of flat membranes produced in accordance with Example 1(d).
- Tables I, II, III and FIGS. 2(a) and 2(b) give data on membrane flux in gallons/day/ft 2 of membrane surface, and solute separation for magnesium sulfate (MgSO 4 ) in dilute aqueous feed solutions at an operating pressure of 100 psig.
- Membranes capable of giving high solute separations for MgSO 4 can be used for several reverse osmosis applications; those giving low separations for MgSO 4 can be used for some reverse osmosis and some ultra-filtration applications; those giving no solute separation for MgSO 4 have relatively large average pore size on the membrane surface, and membrane flux increases with progressive increase in average pore size on membrane surface.
- the latter membranes can be used for a wide variety of ultra-filtration applications; this invention is particularly concerned with these latter membranes.
- the composition and temperature of the casting solution were the same for all the membranes produced in Examples 1 and 2.
- the results given in Tables I, II, III and FIGS. 2(a) and 2(b) show that the membrane flux (and hence the average pore size on the membrane surface) can be changed from about 20 to over 10,000 gallons/day/ft 2 for membranes which can be used for ultra-filtration applications.
- Such wide variation in membrane flux was accomplished by control of solvent evaporation rate prior to gelation (i.e., by the appropriate choice of temperature of casting atmosphere, nature of the casting atmosphere and solvent evaporation period) and also by the control of the gelation conditions with which the present invention is particularly concerned.
- Gelation control is concerned with the choice of the composition and temperature of the gelation medium, and gelation period prior to final leaching in water.
- the gelation medium commonly used in industry is cold water close to 0° C.
- membrane fluxes ranging from 14 to over 10,000 gallons/day/ft 2 can be obtained at 100 psig operating pressure.
- the mole fraction of ethyl alcohol in the gelation medium in the range 0.1 to 1.0, and temperature of gelation medium in the range -20° C. to +30° C. are particularly suitable for making high flux ultra-filtration membranes.
- Solvent evaporation period 5-120 secs. as specified;
- Gelation medium 0-95% ethanol-water mixture as specified
- Temperature of gelation medium -10° to 25° C. as specified;
- FIG. 3 shows the effect of alcohol concentration in the gelation medium on the reverse osmosis performance of membranes resulting from the casting solution. Two sets of membrane performance data are given in FIG. 3; one set of data corresponds to gelation temperature of 0° C., and the other corresponds to gelation temperature of 22° C.
- region 1 The decrease in product rate with corresponding increase in solute separation obtained with these membranes with the initial increase in alcohol concentration in the gelation medium (region 1) is also qualitatively similar to the changes observed by both Zisner and Loeb, 3rd Intern. Symp. on Fresh Water from Sea (Dubrovnik), 2, 615 (1970) and Frommer et al, Ind. Eng. Chem. Prod. Res. Develop., 10, 193 (1971). Since water is the predominant nonsolvent precipitating agent in region 1, following Frommer et al, the above changes may be attributed to the decrease in water activity with increase in alcohol concentration in the gelation medium, and the consequent decrease in the rate of water penetration in the membrane resulting in finer precipitation of polymer material constituting the membrane surface. Thus in region 1, an increase in alcohol concentration in the gelation medium results in a decrease in average pore size on the membrane surface.
- tubular membranes prepared in Examples 1(a) and 2 were tested under ultra-filtration conditions using various solutes, and operating temperatures and pressures, as set forth in Table VI below:
- Length of solvent evaporation zone 12 inches
- Atmosphere above evaporation zone ambient air + acetone
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Dispersion Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
A process for preparing ultra-filtration membranes and the product thereof, in which a selected cellulosic-ester polymer solution is cast into a thin film, at about ambient temperature, partially dried and immersed in a gelation bath at -20 ° to +30° C. The gelation bath contains a sufficient percentage by volume of ethyl alcohol or other organic polar compound to ensure that a flux rate in excess of the initial minimum is achieved. In this way, ultra-filtration membranes having water flux rates selected from within the approximate range 14-10,000 gals./sq.ft./day at 100 psig and a molecular weight cut off above about 15,000, can be produced.
Description
This invention relates to cellulosic-ester semi-permeable membranes, and their preparation and more particularly to semi-permeable membranes for use in ultra-filtration techniques.
Cellulosic-ester polymer semi-permeable membranes have been developed in recent years for use in the process known as reverse osmosis for the separation of solvents and solutes as, for example, in the desalination of sea water, and in the removal of salts, such as nickel chloride, from the effluent of plating processes and the like. In such processes the principal aim is to achieve maximum "rejection" of solute at reasonable "flux." As used in the art, the term "rejection" is defined as the percentage of solute removed, this being determined by the expression (1 - (Cp /Cb)) × 100 where Cp is the concentration of the solute in the solvent after it has passed through the membrane and Cb is the initial solute concentration. Rejection rates in excess of 98% are not uncommon in modern reverse osmosis membrane systems. The term "flux" is defined as the amount of solvent permeating through the membrane per unit surface area per unit time at a constant specified pressure. Flux rates of the order of 40-90 gals./sq.ft./day at 1000 psig operating pressure or 10-50 gals./ft.2 /day at 500 psig, are considered acceptable in most reverse osmosis systems.
Generally, reverse osmosis semi-permeable membranes are produced by casting, from a solution of a cellulosic-ester polymer in a suitable volatile solvent onto a supporting surface, generally a glass or other plate if a flat membrane is required or a tubular sheath if a tubular membrane is required, and allowing the volatile solvent to evaporate partially from the cast membrane and thereafter treating the partially dried cast membrane in a gelation bath with an aqueous solution of a polar compound, organic or inorganic, which does not react chemically with the polymer or the volatile solvent and which is miscible with the volatile solvent, so as to leach out the solvent and any additives from the cast membrane and thereby leave a porous structure in the membrane. Suitable polar compounds include lower alcohols such as methanol, ethanol and propanol; dihydric compounds such as ethylene glycol, trihydric solvents such as glycerine and mixtures of any of the foregoing. It has been found that the pore size can be controlled by, among other parameters, selecting the concentration of the polar compound and hence the flux and rejection characteristics can be modified. As the concentration of the polar compound increases, the flux falls to a minimum and the rejection rate rises to a maximum, depending upon the pressure and the specific compositions involved. We have found that there comes a point, however, where a remarkable and totally unexpected reversal of the aforementioned generalization occurs and which will hereinafter be referred to as the "initial minimum". The rejection rate falls dramatically to a minimum with a relatively small increase in polar compound concentration while the flux rate increases, equally dramatically, from the initial minimum to a first maximum and subsequently continues to increase on a logarithmic scale as the concentration of polar compound in the gelation bath increases beyond that required to produce the initial minimum. In this regard attention is directed to U.S. Pat. No. 3,412,184 issued Nov. 19, 1968 to Sharples and Banks and to British Pat. No. 1,272,574 published May 3, 1972 in the names of Carter and Psaras. According to the prior art, in the production of reverse osmosis membranes, alcohol concentrations up to about 50 grams per 100 cc. of solution (about 55% by volume) may be employed in the gelation bath, it being noted that, for the particular compositions tested an increase in the alcohol concentration reduces the membrane's permeability, i.e. reduces the flux, while increasing the solute rejection efficiency. It is quite clear, therefore, that in the prior art referred to, the concentration of the polar compound never exceeds that required to produce the initial minimum. Further, the prior art teaches that reducing pressure reduces flux.
Other uses for semi-permeable membranes require flux and rejection characteristics quite different from those generally required for reverse osmosis. For example, ultra-filtration membranes, used industrially for such purposes as the treatment of oily waste waters for pollution control, blood dialysis and treatment of mineral tailings ideally require both high rejection rates (of the order of 96%) and high throughputs, i.e. flux rates of the order of 100 to 10,000 gals./ft.2 /day at operating pressures of the order of 100 psi or lower.
It will be appreciated that, in ultra-filtration, the size of the "solute" is generally far larger than that in reverse osmosis systems and such "solute" may be organic or inorganic. Generally organic "solutes," such as starch, vitamins, proteins and the like have extremely high molecular weights (in excess of 15,000) but in certain circumstances relatively low molecular weight compounds, such as oils, may be successfully treated. Ultra-filtration techniques can also be applied to colloidal suspensions, mixtures and emulsions which include oils, inorganic materials such as finely divided coal or mineral tailings, and the like.
It is an object of the present invention to provide an ultra-filtration membrane having a flux rate selected from within the approximate range 14-10,000 gals./sq. ft./day at 100 psig which will separate relatively large solutes such as those having a molecular weight in excess of about 15,000.
Another object of the present invention is to provide a process for producing an ultra-filtration membrane having a flux rate selected from within the approximate range 14-10,000 gals/sq. ft./day at 100 psig, at high rejection rates for selected solutes.
Thus, by one aspect of this invention there is provided in a process for producing a cellulosic ester semi-permeable membrane wherein a thin film is cast from a mixture comprising cellulosic ester polymer, pore forming additive and casting solvent, a portion of the casting solvent is removed from the film and the film is immersed in a gelation bath containing a polar organic compound which is miscible with said casting solvent, the improvement, for producing an ultra-filtration membrane, comprising controlling the temperature of said gelation bath at a selected temperature in the range -20° C. to +30° C. and selecting the concentration of said polar compound in said gelation bath to be greater than that required to produce the initial minimum flux for said membrane.
By another aspect of this invention there is provided a cellulosic ester ultra-filtration membrane, produced as hereinabove defined, having a flux rate in the range 14-10,000 gals./sq. ft./day at 100 psig.
The invention will be described in more detail hereinafter with reference to the examples and accompanying drawings in which:
FIG. 1 is a graph illustrating flux and rejection rates (for NaCl at 1000 psig) according to the prior art;
FIG. 2(a) is a graph relating product rate (flux in gal./sq. ft./day at 100 psig) against ethyl alcohol content of the gelation bath, at various gelation bath temperatures,
FIG. 2(b) is a similar graph showing MgSO4 separation against ethyl alcohol content of the gelation bath at the gelation bath temperatures illustrated in FIG. 2(a); and
FIG. 3 is a graph similar to FIG. 2(a) relating product rate to ethyl alcohol content for a different membrane system.
As pointed out hereinabove, the use of up to about 55% by volume ethyl alcohol gelation baths for reverse osmosis membranes (25% cellulose acetate/45% acetone/30% formamide), which are generally operated at 500-1000 psig, has been described by Sharples et al who were concerned with achieving the maximum rejection rate for dissolved salts such as NiCl2, NaCl and MgSO4 in aqueous solutions. Typical flux and rejection rates are illustrated in FIG. 1 for NaCl.
FIG. 1 (taken from data in Sharples et al, supra) illustrates that as the percentage of ethyl alcohol in the gelation bath increases towards about 50%, the flux in gals./sq. ft./day at 1000 psig falls to a minimum while at the same time the rejection rate rises to a maximum beyond which further gains in rejection are negligible for the type of solute under consideration. Similar curves for flux and rejection rates at 500 psig have been produced and, as expected, are generally somewhat lower in absolute terms. Even lower values would be anticipated at 100 psig, the pressure level illustrated in FIGS. 2(a) and 2(b).
FIGS. 2(a) and 2(b) are graphs illustrative of the present invention and it will be observed that region A in both FIGS. 2(a) and 2(b) corresponds generally to the shape of the curves illustrated in FIG. 1, i.e. as ethyl alcohol concentration increases the flux falls to a minimum and the rejection rate rises to a maximum, although, at the pressure and with the specific compositions involved, the mole fraction or volume of ethyl alcohol required to achieve the respective minimum and maximum is different. At point B (hereinafter referred to as "the initial minimum"), however, there is a remarkable and totally unexpected reversal. The rejection rate falls dramatically to a minimum with a relatively small increase in alcohol concentration while the flux rate increases, equally dramatically, from the initial minimum to a first maximum and subsequently continues to increase on a logarithmic scale as the concentration (volume %) of ethyl alcohol in the gelation bath increases beyond that required to produce the initial minimum. While it is obvious that membranes treated with relatively high concentrations of ethyl alcohol are not suitable for reverse osmosis applications for the separation of generally relatively low molecular weight solutes, such as inorganic salts, as illustrated by the dramatic fall off in rejection rate for MgSO4, such membranes are of enormous interest for ultra-filtration systems where high flux rates, at relatively low pressures are desired, for selected solutes. It will be appreciated by those skilled in the art that the principles of operation of reverse osmosis and ultra-filtration membranes are not to be confused with the principles of conventional screening. A conventional screen will pass any sized particle smaller than the hole-size of the screen whereas in reverse osmosis and ultra-filtration membranes the pore size is always much larger, often by an order of magnitude, than the size of solute which will pass therethrough and further the mechanism involved can vary from one of repulsion of solute from the pore opening to one of attraction to the side of the pore opening. Mere pore size, i.e. leaching rate by ethyl alcohol or other solvent, is not, therefore, the sole factor in determining the flux and rejection rates of a particular membrane. It is, however, surprising that the inversion at point B in FIGS. 2(a) and 2(b) should occur and, further that the flux rate should increase so dramatically thereafter.
As will be appreciated FIGS. 1 and 2 illustrate product flow or flux rates at pressures which differ by an order of magnitude, and at the lower pressure of FIG. 2, the whole of the curve illustrated in FIG. 1, i.e. up to about 50% ethyl alcohol in the gelation bath, has been compressed into region A, i.e. up to about 20% by volume ethyl alcohol, in FIG. 2. It is believed, therefore, that although pore size and product rate are clearly related, such relationship is not linear and not entirely predictable. It is simply not possible to predict that because ethyl alcohol in amounts up to 50% by volume in a gelation bath yields a reverse osmosis membrane having a high-separation rate for magnesium sulphate at a product rate of the order of 40-100 gals./sq.ft./day at 1000 psig, flux rates, of an order of magnitude or more, higher can be achieved at a pressure of 100 psig merely by increasing the percentage volume of alcohol in the gelation bath. Indeed, the prior art tends to the opposite conclusion. From FIG. 2 it is clear that the temperature of the gelation bath also affects the flux rate of the membrane. Generally, the higher the temperature, in the range -20° C. to +30° C., the greater the flux rate at any selected alcohol percentage concentration, and this is also contrary to the teaching of the prior art.
Although ethyl alcohol is preferred in gelation baths according to the present invention other polar organic compounds such as monohydric alcohols such as methanol, isopropanol, dihydric solvents such as ethylene glycol and trihydric solvents such as glycerine are also suitable. Mixtures of such polar compounds may also be used.
The composition of a cellulosic ester membrane for ultra-filtration use (solvent/polymer and non-solvent/polymer ratios of the order of 4.26 and 1.5) generally differs somewhat from that conventionally employed for reverse osmosis use (solvent/polymer and non-solvent/polymer ratios of the order of 3.01 and 0.495). It has been found that a casting solution comprising:
cellulose acetate: 13-19 wt.%
acetone: 58-68 wt.%
water: 14-22 wt.%
and magnesium perchlorate: 1.3-3.3 wt.%
is suitable, and a preferred composition is
cellulose acetate: 14.8 wt.%
acetone: 63 wt.%
water: 19.9 wt.%
and magnesium perchlorate: 2.3 wt.%
The casting solution for ultra-filtration membranes and reverse osmosis is preferably cast at ambient temperature (about 18°-26° C.). As discussed in detail hereinabove, after solvent evaporation for a short time (of the order of 1 to 15 seconds) the ultra-filtration membrane film is immersed in a gelation bath containing an organic solvent, such as ethyl alcohol, in an amount from 25-100% by volume and preferably 55-95%. The balance of the gelation bath, if any, is conveniently water. The temperature of the gelation bath should be in the range -20° C. to +30° C. and no post heating is generally required.
It will be appreciated that in the following examples, the membranes described therein may be made in either a batch mode or in a continuous mode in which the casting solution is continuously fed onto a casting surface and thereafter gelled and leached on a continuous basis.
A film casting solution comprising:
cellulose acetate E-400-25*: 14.8% by wt.
acetone: 63.0% by wt.
water: 19.9% by wt.
and magnesium perchlorate: 2.3% by wt.
was divided into two portions for the production of (a) one inch diameter tubular membranes and (b) flat membranes, using the conventional casting, drying and gelation steps under the following conditions:
Temperature of casting solution: ˜22° C. (room temperature);
Driving pressure on casting solution: 65 psig;
Film casting speed: one inch per second;
Air flow rate: 28 cc/sec.;
Temperature of solvent evaporation zone: ˜22° C. (room temperature);
Length of solvent evaporation zone: 6 to 15 inches as indicated;
Atmosphere of above zone: air, or air + acetone vapor or air + (acetone + water) vapor as indicated;
Gelation bath: flowing water, or acetone + water mixture or ethyl alcohol + water mixture, as indicated;
Temperature of gelation bath: 0° to 22° C. as indicated;
Gelation time: 10 to 60 minutes as indicated;
Leaching bath: water at 0° to 1° C.;
Leaching time: 1 hour.
Temperature of casting solution: ˜22° C. (room temperature);
Temperature of solvent evaporation atmosphere: ˜22° C. (room temperature);
Solvent evaporation atmosphere: air, or air + (acetone + water) vapor, as indicated;
Solvent evaporation time: 0 to 5 seconds;
Gelation bath: water or (ethyl alcohol + water) mixture as indicated;
Temperature of gelation bath: -15° to +20° C. as indicated;
Gelation time: 15 minutes;
Leaching bath: water at ˜1° C.;
Leaching time: 1 hour;
Temperature of casting solution: ˜22° C. (room temperature);
Temperature of solvent evaporation atmosphere: ˜22° C. (room temperature);
Solvent evaporation atmosphere: ambient air, relative humidity: 85-90%;
Solvent evaporation time: 0 to 5 seconds;
Gelation bath: water, or (ethyl alcohol + water) mixture or absolute ethyl alcohol as indicated;
Temperature of gelation bath: -20° C. to 30° C. as indicated;
Gelation time: 10 minutes;
Leaching bath: water at ˜1° C.;
Leaching time: 1 hour.
Gelation bath: 50% (by volume) of methanol, ethanol, isopropanol, or ethylene glycol in water-alcohol mixture;
Temperature of gelation bath: 20° C.;
All other conditions same as in Example 1(c).
Samples of the tubular and flat membranes prepared in Examples 1(a), 1(b), 1(c) and 1(d) were tested for reverse osmosis performance at 100 psig operating pressure with a feed solution containing 300 ppm magnesium sulphate-water, at a feed flow rate of 500 cc/min. Table I hereinbelow tabulates the results of a set of 4 ft. long, one-inch diameter tubular membranes, prepared in accordance with Example 1(a).
TABLE I __________________________________________________________________________ Data forSet 1 Tubular Membranes Film Casting Conditions T1* T2 T3 T4 T5 T6 T7 T8 __________________________________________________________________________ Length of solvent evaporation 6" 12" 12" 12" 15" 15" 15" 15" zone Atmosphere Air + Air + Air + Air + Air + of above 50/50 50/50 50/50 pure 50/50 evaporation acetone/ acetone/ acetone/ acetone acetone/ Air Air Air zone H.sub.2 O vap. H.sub.2 O vap. H.sub.2 O vap. vap. H.sub.2 O vap. Gelation 5% 33% 33% 50% 50% bath water water acetone water EtOH- EtOH- EtOH- EtOH- water water water water water Temp. ofgelation 1° C. 1° C. 8° C. 1° C. ≈0° C. ≈0° C. ≈0° C. 20° C.bath Gelation time 60 min. 60 min. 15 min. 60 min. 10 min. 10 min. 10 min. 10 min. Solute Separation % 71 85 62 89 28 11 1 ≈0 Water flux, very gal/day ft.sup.2 35.8 33 26.9 40 90 107 200 high __________________________________________________________________________ *Air flow rate: 14 cc/sec
Table II sets forth comparable data in respect of flat membranes prepared in accordance with Example 1(b).
Table II ______________________________________ Data forSet 2 Flat Membranes Film Casting Conditions F1 F2 F3 F4 F5 ______________________________________ Solvent evaporation Air Air Air AirAir atmosphere Gelation 20% 33% 33% bath Water Water EtOH- EtOH- EtOH- Water Water Water Temp. of gelation 21° C. 1° C. 7° C. -15° C. +15° C. bath Solute separation, % 85 70 75 20 15.5 water flux gal/day ft.sup.2 35.8 71.6 58 89 100 ______________________________________
FIGS. 2(a) and 2(b) set forth data in respect of flat membranes prepared in accordance with Example 1(c) and Table III sets forth data in respect of flat membranes produced in accordance with Example 1(d).
Table III
______________________________________
Data for Set 4 Flat Membranes
Solute Water Flux
Gelation Bath Separation, %
gal/day/ft.sup.2
______________________________________
Methanol (50%)-Water
3.3 468
Ethanol (50%)-Water
0.1 988
Isopropanol (50%)-Water
0 450
Ethylene glycol (50%)-Water
84.5 9
______________________________________
Tables I, II, III and FIGS. 2(a) and 2(b) give data on membrane flux in gallons/day/ft2 of membrane surface, and solute separation for magnesium sulfate (MgSO4) in dilute aqueous feed solutions at an operating pressure of 100 psig. Membranes capable of giving high solute separations for MgSO4 can be used for several reverse osmosis applications; those giving low separations for MgSO4 can be used for some reverse osmosis and some ultra-filtration applications; those giving no solute separation for MgSO4 have relatively large average pore size on the membrane surface, and membrane flux increases with progressive increase in average pore size on membrane surface. The latter membranes can be used for a wide variety of ultra-filtration applications; this invention is particularly concerned with these latter membranes.
The composition and temperature of the casting solution were the same for all the membranes produced in Examples 1 and 2. The results given in Tables I, II, III and FIGS. 2(a) and 2(b) show that the membrane flux (and hence the average pore size on the membrane surface) can be changed from about 20 to over 10,000 gallons/day/ft2 for membranes which can be used for ultra-filtration applications. Such wide variation in membrane flux was accomplished by control of solvent evaporation rate prior to gelation (i.e., by the appropriate choice of temperature of casting atmosphere, nature of the casting atmosphere and solvent evaporation period) and also by the control of the gelation conditions with which the present invention is particularly concerned.
Gelation control is concerned with the choice of the composition and temperature of the gelation medium, and gelation period prior to final leaching in water. The gelation medium commonly used in industry is cold water close to 0° C.
From FIGS. 2(a) and 2(b) it will be apparent that by appropriate combination of ethyl alcohol content in the gelation medium, and the temperature of the gelation medium, membrane fluxes ranging from 14 to over 10,000 gallons/day/ft2 can be obtained at 100 psig operating pressure. The mole fraction of ethyl alcohol in the gelation medium in the range 0.1 to 1.0, and temperature of gelation medium in the range -20° C. to +30° C. are particularly suitable for making high flux ultra-filtration membranes.
The data given in Table III show that the use of methanol, isopropanol, or ethylene glycol instead of ethanol in the gelation medium gives similar results; the use of ethanol is superior to the other alcohols tested for making high flux ultra-filtration membranes.
Flat membranes were cast under the following conditions from a solution comprising (wt.%):
cellulose acetate (E-398-3): 25.0
acetone: 45.0
formamide: 30.0
Temperature of casting solution: 25° C.;
Temperature of casting atmosphere: 25° C.;
Humidity of casting atmosphere: 50%;
Solvent evaporation period: 5-120 secs. as specified;
Gelation medium: 0-95% ethanol-water mixture as specified;
Temperature of gelation medium: -10° to 25° C. as specified;
Gelation period: 1 hour.
This composition corresponds to that employed by Carter et al (supra). All membranes were hand cast as flat films on glass plates in a constant temperature-constant humidity room. All films were subjected to a pure water pressure of 300 psig for at least one hour prior to testing. All testing was carried out at 250 psig, 23°-26° C. using 3500 ppm sodium chloride-water as the feed solution at a constant feed flow rate of 400 cm3 /min. FIG. 3 shows the effect of alcohol concentration in the gelation medium on the reverse osmosis performance of membranes resulting from the casting solution. Two sets of membrane performance data are given in FIG. 3; one set of data corresponds to gelation temperature of 0° C., and the other corresponds to gelation temperature of 22° C. The data on membrane performance corresponding to both the above gelation temperatures fall into three distinct regions. At the gelation temperature of 0° C., in region 1, product rate decreases from 185 to 50 g/hr and the corresponding solute separation increases from 8 to 23% with increase in alcohol concentration in the gelation medium up to ˜33%; in region 2, product rate increases from 50 to 220 g/hr and the corresponding solute separation decreases from 23 to 1% with increase in alcohol concentration from 33 to 57%; and in region 3, product rate decreases from 220 to 90 g/hr and the corresponding solute separation increases from 1 to 25% with increase in alcohol concentration from 57 to 95%. At the gelation temperature of 22° C., in region 1, product rate decreases from 90 to 25 g/hr and the corresponding solute separation increases from 10 to 65% with increase in alcohol concentration up to ˜30%; in region 2, product rate increases from 25 to 730 g/hr and the corresponding solute separation decreases from 65 to 1% with increase in alcohol concentration from ˜30 to 71%; and in region 3, product rate decreases from 730 to 310 g/hr and the corresponding solute separation increases from 1 to 4% with increase in alcohol concentration from 71 to 95%. Thus the data on membrane performance in the above three regions are similar in effect and quite different in magnitude at the two gelation temperatures.
Carter et al (supra) used this casting solution composition and alcohol concentrations up to 8.7 molar (which is less than 50% alcohol by volume) in the gelation medium at 20° C. Under the conditions of their experiments, product rate decreased and the corresponding solute separation increased with increase in alcohol concentration. These results are qualitatively similar to those obtained in region 1 for the present casting solution composition given in FIG. 3.
The decrease in product rate with corresponding increase in solute separation obtained with these membranes with the initial increase in alcohol concentration in the gelation medium (region 1) is also qualitatively similar to the changes observed by both Zisner and Loeb, 3rd Intern. Symp. on Fresh Water from Sea (Dubrovnik), 2, 615 (1970) and Frommer et al, Ind. Eng. Chem. Prod. Res. Develop., 10, 193 (1971). Since water is the predominant nonsolvent precipitating agent in region 1, following Frommer et al, the above changes may be attributed to the decrease in water activity with increase in alcohol concentration in the gelation medium, and the consequent decrease in the rate of water penetration in the membrane resulting in finer precipitation of polymer material constituting the membrane surface. Thus in region 1, an increase in alcohol concentration in the gelation medium results in a decrease in average pore size on the membrane surface.
As the alcohol concentration in the gelation medium increases further into the regions 2 and 3 in FIG. 3, the polymer precipitating power of alcohol and its interactions with the polymer (cellulose acetate), solvent (acetone), and nonsolvent-swelling agent (aqueous magnesium perchlorate or formamide) in the membrane matrix become progressively more important. These factors could affect both the precise instant of phase inversion and also the size, number and distribution of nonsolvent droplets (incipient voids) in the interdispersed phase during gelation, which ultimately determine the surface pore structure of the resulting membrane. The general increase in product rate with increase in alcohol concentration in the gelation medium in regions 2 and 3 in FIG. 3, and the existence of maxima and minima in product rate and solute separation data in the above regions indicate that the above factors include those having opposing tendencies in the direction of change of size, number and distribution of pores on the membrane surface and the effective thickness of the membrane.
The tubular membranes prepared in Examples 1(a) and 2 (Table I) were tested under ultra-filtration conditions using various solutes, and operating temperatures and pressures, as set forth in Table VI below:
TABLE IV
______________________________________
Oper.
ating Oper-
pres- ating Solute
Membrane
Mem- sure, temp. separa-
flux
brane Feed Details psig ° C.
tion, %
gal/day/ft.sup.2
______________________________________
T5 Pure water
permeation 20 25 -- 19.8
rate 20 34 -- 22.8
Cutting oil
emulsion # 2; 20 26 19.4
oil concentra-
20 30 20.9
tion ≈10% by
20 40 23.6
weight; con- 20 42 95 25.1
centrate and 20 40 24.3
product recycl-
20 49 28.9
ed. pH = 6.5 20 39 23.2
Cutting oil
emulsion # 2
initial oil 20 33 99 20.5
concentration
20 34 99 21.3
in feed ≈12%
20 33 99 20.5
weight; final
20 33 99 20.5
oil concentra-
20 30 99 21.3
tion in the 20 29 99 17.1
feed at the end
of run ≈24%.
pH = 6.5
Pure water
permeation rate
20 34 -- 22.8
after soap 20 30 -- 19.0
cleaning
T6 100 ppm Magne-
sium sulfate-
25 30 13.7 13.5
water 25 64 11.9 23.4
Cutting oil
emulsion # 1 oil
content:
1.2% 10 45 95 11.6
10.0% 20 62 96 25.4
24.0% 20 46 98 20.4
100 ppm Magne-
sium sulfate-
25 30 8.4 15.0
water
T6 Pure water 20 17 -- 16.2
permeation 20 24 -- 19.8
rate 20 28 -- 20.9
20 34 -- 23.2
Cutting oil
emulsion # 2,
oil content 20 33 90 18.3
≈10% increas-
20 48 90 25.5
ed slightly 20 65 90 23.6
during the run. (Product
pH = 6.5 highly
colored
due to
emulsifier)
T7 Pure water 20 15 -- 13.6
permeation 20 30 -- 19.9
rate 20 43 -- 22.6
20 49 -- 27.3
20 55 -- 31.7
20 60 -- 34.6
Cutting oil
emulsion #1
20 gallons
concentrated
to 9 gallons;
feed was not
of uniform
consistency
oil content:
0.32% 20 29 93 16.1
0.5% 20 59 93 33.7
0.64% 20 58 93 32.5
14.4% 20 32 94.8 17.8
28.8% 20 62 97.0 27.9
36.4% 20 30 98.2 16.8
45% 20 53 99.3 28.8
48% 20 59 99.9 15.4
50% 20 49 100 5.5
18 hour run;
feed flow rate:
1100 gal/hr;
membrane area:
1 ft.sup.2
T8 Pure water 11 38 -- 79.4
permeation 15 40 -- 118.0
rate 20 40 -- 158.0
3% potato
starch sus- 11 40 100 79.0
pension in 15 40 100 112.5
water 20 40 100 114.5
T8 Alberta clay
suspension in
11 44 100 91.3
water, 5% 15 48 100 128.5
bentonite 21 50 100 168.7
T8D Pure water
(drop permeation 10 42 -- 139
method
rate
of cast-
ing) Cutting oil
emulsion #1, 10 60 90 28.5
oil content 22 56 75 47.5
5%, pH = 6 (membrane
fouled)
T8D Pure water 11 40 -- 30.8
(drop permeation 15 40 -- 45.6
method
rate 20 40 -- 62.7
of cast-
ing) Potato starch
suspension in
water; starch
content:
100 grams/5 gal.
11 40 100 28.5
15 37 100 40.2
20 37 100 53.2
200 grams/5 gal.
11 40 100 29.3
15 41 100 41.8
20 41 100 57.0
3% by weight 20 40 100 54.0
T10 Pure water 20 20 -- 152
permeation 20 25 -- 164
rate 20 28 -- 168
20 30 -- 180
Water slurry con-
sisting of coal
tailings made up
of 50% coal and
50% ash:
Solids content
in feed:
0% 20 30 100 180
T10 10% 20 30 100 168
20% 20 30 100 162
30% 20 30 100 153
35% 20 30 100 149
40% 20 30 100 140
45% 20 30 100 114
50% 20 30 100 62
______________________________________
(t10 membrane was similar to those described in Example 1(a) and was made under the following conditions:
Length of solvent evaporation zone: 12 inches;
Atmosphere above evaporation zone: ambient air + acetone;
Gelation bath: 95% Ethyl alcohol-water;
Temperature of gelation bath: 20° C.;
Gelation time: 10 minutes.)
Claims (13)
1. In a process for producing a cellulosic ester semi-permeable membrane wherein a thin film is cast from a mixture comprising cellulosic ester polymer, pore-forming additive and casting solvent, a portion of the casting solvent may be removed from the film and the film is immersed in a gelation bath containing a polar organic compound which is miscible with said casting solvent, the improvement, for producing an ultra-filtration membrane, comprising controlling the temperature of said gelation bath at a selected temperature in the range -20° C. to +30° C. and selecting said polar organic compound to be an alcohol in a concentration, in said gelation bath greater than that required to produce an initial minimum flux for said membrane, equivalent to point B in FIG. 2a.
2. A process as claimed in claim 1 wherein said alcohol is selected from the group comprising lower monohydric alcohols, dihydric alcohols, trihydric alcohols and mixtures thereof.
3. A process as claimed in claim 2 wherein said gelation bath comprises an aqueous solution of said alcohol.
4. A process as claimed in claim 3 wherein said alcohol in said solution is present in an amount from 25-100% by volume.
5. A process as claimed in claim 4 wherein said gelation bath comprises 25-95% by volume ethyl alcohol in water.
6. A process as claimed in claim 4 wherein said thin film is cast at a temperature in the range 18°-26° C.
7. A process as claimed in claim 6 wherein said gelation bath is at a temperature in the range -20° to +30° C.
8. A process as claimed in claim 1 wherein said film is immersed in a separate leaching bath following said gelation bath.
9. A cellulosic ester ultra-filtration membrane produced by the process of claim 1 having a water flux rate in the range 14-10,000 gals/sq.ft./day at 100 psig, and a magnesium sulphate rejection at 100 psig below about 40%.
10. An ultra-filtration membrane as claimed in claim 9 wherein said film is cast from a mixture comprising:
13-19 weight % cellulose acetate
58-68 weight % acetone
14-22 weight % water
1.3-3.3 weight % magnesium perchlorate.
11. An ultra-filtration membrane as claimed in claim 10 having a molecular weight cut off in excess of about 15,000.
12. A process as claimed in claim 2 wherein said alcohol is selected from the group consisting of ethyl alcohol, methyl alcohol and mixtures thereof.
13. A process as claimed in claim 7 wherein said gelation bath is at a temperature in the range 0° C. to 20° C.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/824,642 US4145295A (en) | 1977-08-15 | 1977-08-15 | Cellulose ester ultra-filtration membranes and their manufacture |
| CA000309230A CA1090956A (en) | 1977-08-15 | 1978-08-14 | Ultra-filtration membranes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/824,642 US4145295A (en) | 1977-08-15 | 1977-08-15 | Cellulose ester ultra-filtration membranes and their manufacture |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US4145295A true US4145295A (en) | 1979-03-20 |
Family
ID=25241942
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US05/824,642 Expired - Lifetime US4145295A (en) | 1977-08-15 | 1977-08-15 | Cellulose ester ultra-filtration membranes and their manufacture |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4145295A (en) |
| CA (1) | CA1090956A (en) |
Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4234528A (en) * | 1978-04-13 | 1980-11-18 | Sartorius Gmbh | Asymmetrical ultrafiltration membrane based on cellulose hydrate |
| US4496456A (en) * | 1983-06-03 | 1985-01-29 | Exxon Research & Engineering Co. | Method for preparing thin regenerated cellulose membranes of high flux and selectivity for organic liquids separations |
| US4541972A (en) * | 1983-12-14 | 1985-09-17 | Exxon Research And Engineering Co. | Preparation of cellulose acetate membrane and its use for polar solvent-oil separation |
| US4609728A (en) * | 1983-06-15 | 1986-09-02 | Gambro Dialysatoren Kg | Method of treating a cellulosic hollow fiber |
| EP0207721A2 (en) | 1985-06-27 | 1987-01-07 | A/G Technology Corporation | Anisotropic membranes for gas separation |
| US4678555A (en) * | 1983-12-14 | 1987-07-07 | Exxon Research And Engineering Company | Preparation of cellulose acetate membrane and its use for polar solvent-oil separation |
| EP0339502A2 (en) * | 1988-04-28 | 1989-11-02 | Akzo Nobel N.V. | Process for modifying cellulosic membrances for the improvement of their biocompatibility, and apparatus for carrying out the process |
| US5897817A (en) * | 1992-11-16 | 1999-04-27 | Althin Medical, Inc. | Process for making a medical device from a cellulose acetate hollow fiber semipermeable membrane |
| US20020096668A1 (en) * | 2000-11-28 | 2002-07-25 | Vandersall Howard L. | Fire retardant compositions with reduced aluminum corrosivity |
| US20030038081A1 (en) * | 2001-08-14 | 2003-02-27 | I-Fan Wang | High strength asymmetric cellulosic membrane |
| US20030066990A1 (en) * | 2000-11-28 | 2003-04-10 | Vandersall Howard L. | Ammonium polyphosphate solutions containing multi-functional phosphonate corrosion inhibitors |
| US20050040101A1 (en) * | 2001-08-17 | 2005-02-24 | Jianfeng Kong | Hollow fiber membrane for the treatment of waste lubricants and method for its production |
| CN114653214A (en) * | 2022-03-29 | 2022-06-24 | 赛普(杭州)过滤科技有限公司 | Preparation method of regenerated cellulose ultrafiltration membrane with controllable product performance and product |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3412184A (en) * | 1966-02-17 | 1968-11-19 | Arthur D Little Res Inst | Process for the preparation of cellulosic ester reverse osmosis membranes |
| US3432584A (en) * | 1966-02-17 | 1969-03-11 | Aerojet General Co | Process for the manufacture of a reverse osmosis membrane having a nonheating annealing step |
| US3439074A (en) * | 1965-10-01 | 1969-04-15 | Little Inc A | Method for preparing desalination membranes |
| US3592672A (en) * | 1969-12-22 | 1971-07-13 | Eastman Kodak Co | Dry stabilized,rewettable semipermeable cellulose ester and ether membranes and their preparation |
| US3646179A (en) * | 1969-05-22 | 1972-02-29 | Westinghouse Electric Corp | Process for preparing high pressure cellulose acetate semipermeable membranes |
| GB1272574A (en) * | 1968-04-03 | 1972-05-03 | Nat Res Dev | Improvements in or relating to semipermeable membranes and to the method of preparing same |
| US3957935A (en) * | 1973-12-10 | 1976-05-18 | Hoechst Aktiengesellschaft | Process for the production of a dry desalting cellulose acetate membrane |
-
1977
- 1977-08-15 US US05/824,642 patent/US4145295A/en not_active Expired - Lifetime
-
1978
- 1978-08-14 CA CA000309230A patent/CA1090956A/en not_active Expired
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3439074A (en) * | 1965-10-01 | 1969-04-15 | Little Inc A | Method for preparing desalination membranes |
| US3412184A (en) * | 1966-02-17 | 1968-11-19 | Arthur D Little Res Inst | Process for the preparation of cellulosic ester reverse osmosis membranes |
| US3432584A (en) * | 1966-02-17 | 1969-03-11 | Aerojet General Co | Process for the manufacture of a reverse osmosis membrane having a nonheating annealing step |
| GB1272574A (en) * | 1968-04-03 | 1972-05-03 | Nat Res Dev | Improvements in or relating to semipermeable membranes and to the method of preparing same |
| US3646179A (en) * | 1969-05-22 | 1972-02-29 | Westinghouse Electric Corp | Process for preparing high pressure cellulose acetate semipermeable membranes |
| US3592672A (en) * | 1969-12-22 | 1971-07-13 | Eastman Kodak Co | Dry stabilized,rewettable semipermeable cellulose ester and ether membranes and their preparation |
| US3957935A (en) * | 1973-12-10 | 1976-05-18 | Hoechst Aktiengesellschaft | Process for the production of a dry desalting cellulose acetate membrane |
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4234528A (en) * | 1978-04-13 | 1980-11-18 | Sartorius Gmbh | Asymmetrical ultrafiltration membrane based on cellulose hydrate |
| US4496456A (en) * | 1983-06-03 | 1985-01-29 | Exxon Research & Engineering Co. | Method for preparing thin regenerated cellulose membranes of high flux and selectivity for organic liquids separations |
| US4609728A (en) * | 1983-06-15 | 1986-09-02 | Gambro Dialysatoren Kg | Method of treating a cellulosic hollow fiber |
| US4541972A (en) * | 1983-12-14 | 1985-09-17 | Exxon Research And Engineering Co. | Preparation of cellulose acetate membrane and its use for polar solvent-oil separation |
| US4678555A (en) * | 1983-12-14 | 1987-07-07 | Exxon Research And Engineering Company | Preparation of cellulose acetate membrane and its use for polar solvent-oil separation |
| EP0207721A2 (en) | 1985-06-27 | 1987-01-07 | A/G Technology Corporation | Anisotropic membranes for gas separation |
| EP0339502A2 (en) * | 1988-04-28 | 1989-11-02 | Akzo Nobel N.V. | Process for modifying cellulosic membrances for the improvement of their biocompatibility, and apparatus for carrying out the process |
| EP0339502A3 (en) * | 1988-04-28 | 1989-11-29 | Akzo N.V. | Process for modifying cellulosic membrances for the improvement of their biocompatibility, and apparatus for carrying out the process |
| US5897817A (en) * | 1992-11-16 | 1999-04-27 | Althin Medical, Inc. | Process for making a medical device from a cellulose acetate hollow fiber semipermeable membrane |
| US20020096668A1 (en) * | 2000-11-28 | 2002-07-25 | Vandersall Howard L. | Fire retardant compositions with reduced aluminum corrosivity |
| US20030066990A1 (en) * | 2000-11-28 | 2003-04-10 | Vandersall Howard L. | Ammonium polyphosphate solutions containing multi-functional phosphonate corrosion inhibitors |
| US20030038081A1 (en) * | 2001-08-14 | 2003-02-27 | I-Fan Wang | High strength asymmetric cellulosic membrane |
| US20050040101A1 (en) * | 2001-08-17 | 2005-02-24 | Jianfeng Kong | Hollow fiber membrane for the treatment of waste lubricants and method for its production |
| CN114653214A (en) * | 2022-03-29 | 2022-06-24 | 赛普(杭州)过滤科技有限公司 | Preparation method of regenerated cellulose ultrafiltration membrane with controllable product performance and product |
Also Published As
| Publication number | Publication date |
|---|---|
| CA1090956A (en) | 1980-12-09 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4145295A (en) | Cellulose ester ultra-filtration membranes and their manufacture | |
| US3988245A (en) | Anisotropic polyvinyl formal resin microporous membrane and its preparation | |
| US3580841A (en) | Ultrathin semipermeable membrane | |
| US5988400A (en) | Pourous fluorocarbon membrane, method for producing thereof and cartridge filter based on said membrane | |
| US4737325A (en) | Composite semipermeable membrane and process for preparation thereof | |
| US5342521A (en) | Reverse osmosis or nanofiltration membrane and its production process | |
| US4933081A (en) | Asymmetric micro-porous membrane containing a layer of minimum size pores below the surface thereof | |
| US2953502A (en) | Separation of azeotropic mixtures | |
| US3549016A (en) | Permeable membrane and method of making and using the same | |
| US3884801A (en) | Preparation of reverse osmosis membranes by complete evaporation of the solvent system | |
| US3780147A (en) | Method for making high flow porous reverse osmosis membranes containing lipids | |
| US4147622A (en) | Process for manufacturing membranes for osmotic separation | |
| US4925566A (en) | Ultrafiltration, hyperfiltration or demineralization element, its production process and its use for the treatment of liquid radioactive effluents | |
| US4806291A (en) | Process for preparing microporous polyvinylidene fluoride membranes | |
| JPS5857203B2 (en) | Ultrafiltration membrane made of linear polyurethane, its manufacturing method, and method for separating oil from water | |
| US3483282A (en) | Production of semipermeable membranes | |
| DE1794191A1 (en) | Microporous membrane | |
| US3676203A (en) | Semipermeable membranes | |
| US3666508A (en) | High flux semipermeable cellulosic derivative membranes with dry handling capabilities and their method of preparation | |
| EP0880400A1 (en) | Composite membrane with a support membrane made, in particular of microporous material | |
| US3439074A (en) | Method for preparing desalination membranes | |
| US3718722A (en) | A method of forming a porous cellulose acetate membrane | |
| US4775703A (en) | Process for preparing microporous polyvinylidene fluoride membranes | |
| US3536612A (en) | Increasing permeability of reverse osmosis membranes | |
| US3544455A (en) | Itaconic acid purification process using reverse osmosis |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| AS | Assignment |
Owner name: NATIONAL RESEARCH COUNCIL OF CANADA, CANADA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:CANADIAN PATENTS AND DEVELOPMENT LIMITED SOCIETE CANADIENNE BREVETS ET D EXPLOITATION LIMITEE;REEL/FRAME:006057/0686 Effective date: 19920102 |